1. Field of the Invention
The present invention relates to an optoelectronic transmitter integrated circuit and method of fabricating the same and, more specifically, to an optoelectronic transmitter integrated circuit having an integrated single chip structure in which an absorption layer of an electroabsorption (EA) modulator and a quantum well (QW) layer of a double heterojunction bipolar transistor (DHBT) have different thicknesses, and method of fabricating the same using a selective MOCVD (Metal Organic Chemical Vapor Deposition) growth method.
2. Discussion of Related Art
A conventional long-wavelength optical transmitter integrated circuit in which a semiconductor laser and a DHBT are integrated is widely used in optical communication systems. In general, such an optical transmitter integrated circuit is fabricated by growing the semiconductor laser structure on a substrate and then growing the DHBT structure on the substrate on which the semiconductor laser is grown.
In the conventional optical transmitter integrated circuit in which the semiconductor laser is integrated, when a driving current is supplied to an active layer to drive the semiconductor laser, the refractive index of the active layer is changed so that oscillation wavelength fluctuates (this is generally termed “chirping”) and thus, modulation speed is limited. For this reason, the conventional optical transmitter integrated circuit cannot be readily utilized for high-speed and long-distance optical communications.
In another case, the conventional optical transmitter integrated circuit may include an electroabsorption (EA) modulator in place of a semiconductor laser. In this case, when a reverse bias voltage is applied to a quantum well absorption layer, a quantum confined stark effect (QCSE) occurs so that the absorption band wavelength of light is changed. That is, because no chirping takes place unlike in the semiconductor laser, the optical transmitter integrated circuit in which the EA modulator is integrated can be used for high-capacity long-distance optical communications. However, since a conventional pin type EA modulator has the same epitaxial crystal structure as a DHBT consisting of p+-base, i-collector and n+-sub collector, it cannot have an independent epitaxial structure and optimize its characteristics. Thus, it is difficult to further improve the modulation efficiency and driving characteristic of the optical transmitter integrated circuit (IC).